The modern world is called a stressful society, and there has been a strong demand for a method for objective fatigue measurement or evaluation for everyday use. In the past, quantitative fatigue evaluation (flicker test) was performed based on a phenomena in which the perception of “flicker” upon observation of a blinking light source changes depending on the fatigue degree; in particular, a phenomena in which the blinking frequency (Critical Flicker Frequency: CFF), which denotes the capability of perceiving a flicker, decreases along with an increase of fatigue degree. Heretofore, quantitative evaluation of fatigue degree using a flicker test has been widely employed, particularly in the industrial hygiene field. However, because this flicker test requires a dedicated device equipped with an LED or the like, it was not suitable for a universal or everyday use device.
Under such circumstances, the inventors of the present invention developed a technology for enabling a fatigue degree test, which is based on the same flicker perception principle as in the flicker test, but which uses an image-displaying device such as a CRT or a liquid crystal display (see Patent Literature 1 below). The development of such a device enables, in principle, easy fatigue measurement on a daily basis using easily accessible devices, such as mobile phones or personal computers.